The use of forming shoes having a solid forming surface adapted to contact one of the wires on a twin wire former while squeezing water out through the other wire are well known. One such device is shown in U.S. Pat. No. 4,033,812, issued July 5, 1977 to Graham Riihinen. The particular device shown in this patent is primarily adapted for the formation of tissue paper and incorporates a first open drainage section through a single open stretch bottom wire and then through a twin wire section wherein the wires pass around a solid shoe and water is ejected through the upper wire.
A somewhat similar device is shown in Canadian Pat. No. 930,580 issued July 24, 1973 to McCormack. However, in this device, no significant preforming section is used and substantially all of the drainage takes place upwardly through the top wire with the water drained therefrom being scooped from the top wire and directed into a saveall. This former is primarily concerned with multi-ply papermaking or boardmaking machines.
In both of these devices the wire contacting the forming surface is directed across the forming surface of a shoe which inherently causes wear of the wire.
Obviously the wear on the wire is depended in part on the amount of lubricant that passes between the wire and the surface of the shoe, and thus the wetter the web, the greater the lubrication that is available. In the U.S. Patent, predrainage occurs through the bottom wire before the shoe is reached. Thus, there is a formed layer of stock on the bottom wire which contacts the shoe when the wire traverses the shoe. Obviously, this layer of formed fibres will inhibit flow of water or drainage of water towards the shoe and thereby reduce the amount of lubricant that is available. In the Canadian Patent, very little predrainage takes place and the majority of the formation takes place against the wire remote from this forming surface, thus the problem of lubricating the wire-shoe surface interface is reduced since there is no mat therebetween. However, there is still the significant wear factor encountered and drainage may be improved.